Increased immunoglobulin binding to cerebral endothelium in patients with antiphospholipid antibodies

There is a strong link between antiphospholipid antibodies and stroke. The mechanism of action of antiphospholipid antibodies is unknown. Most theories of pathogenesis center around platelet or endothelial cell dysfunction. Our aim was to determine if there were immunoglobulins in the sera of patients with antiphospholipid antibodies that bind human brain microvascular endothelial cells. We studied sera from three groups of subjects: patients with antiphospholipid antibodies and stroke (group 1), healthy control subjects (group 2), and patients with stroke but without antiphospholipid antibodies (group 3). We isolated human brain microvascular endothelial cells from temporal lobectomy specimens and used a cellular enzyme-linked immunosorbent assay (ELISA) to measure immunoglobulin binding to endothelial cells derived from human brain and from human umbilical vein. We used a chromium release assay to measure cytotoxicity. Patients with antiphospholipid antibodies and stroke had significantly higher immunoglobulin binding to human brain microvascular endothelial cells than subjects in the other groups ([ELISA index+standard deviation], 63 +/- 37 [group 1] versus 7 +/- 7 [group 2] versus 7 +/- 7 [group 3], P < .001). There was, however, poor correlation between binding to brain endothelial cells and binding to cardiolipin. The binding to brain microvascular cells was not specific to brain endothelium, as similar results were found in an ELISA using human umbilical vein cells. There was no evidence of complement-mediated brain endothelial cell cytotoxicity. Patients with stroke and antiphospholipid antibodies frequently have human brain microvascular endothelial-reactive antibodies in their serum. These antibodies are distinct from those to cardiolipin. We found no evidence that these antibodies are cytotoxic.